Hereinafter, a carrier will be described in brief.
The user may have information for which modulation manipulation on the amplitude, frequency and/or phase of a sine wave or periodic pulse wave is performed to be transmitted. At this time, the sine wave or pulse wave performing the role of carrying information may be referred to as a carrier.
The scheme of modulating a carrier may include a single-carrier modulation (SCM) scheme and a multi-carrier modulation (MCM) scheme. Of them, the single-carrier modulation scheme is a modulation method of loading all information on a carrier to modulate them.
The multi-carrier modulation scheme refers to a technology in which an entire bandwidth channel of one carrier is divided into sub-channels having several small bandwidths and multiple narrowband sub-carriers are transmitted in a multiplexed manner through each sub-channel.
At this time, when using a multi-carrier modulation (MCM) scheme, each sub-channel may be approximated to a flat characteristic (flat channel) due to its small bandwidth. Furthermore, the user may compensate the distortion of the channel using a simple equalizer. Furthermore, the multi-carrier modulation scheme enables high-speed implementation using fast Fourier transformation (FFT). In other words, it may be advantageous in high-speed data transmission compared to the single-carrier modulation scheme.
As the performance of the base station and/or terminal is developed, the range of the frequency bandwidth provided or used by the base station and/or terminal is expanded. Therefore, according to an embodiment of the present disclosure, there is disclosed a multicarrier system for supporting broadband by aggregating one or more carriers.
In other words, the multicarrier system to be described below illustrates a case where one or more carriers are aggregated to be used, contrary to the multi-carrier modulation scheme in which one carrier is divided to be used as described above.
The technology of managing several carriers (for example, several frequency carriers (FCs)) with one medium access control (MAC) entity has been proposed to effectively use multi-band (or multi-carrier).
FIGS. 1A and 1B are views illustrating a multi-band radio frequency (RF) based signal transmission and reception method.
In FIG. 1, one medium access control layer at the transmission and reception ends can manage several carriers to effectively use a multicarrier. At this time, in order to effectively transmit and receive a multicarrier, it is assumed that both the transmission and reception ends can transmit and receive a multicarrier. At this time, frequency carriers (FCs) managed by one medium access control layer are not required to be contiguous to one another, and thus it has flexibility in the aspect of resource management. In other words, both contiguous aggregation and non-contiguous aggregation may be allowed.
According to FIGS. 1A and 1B, physical layer (PHY) 0, physical layer 1, . . . , physical layer n-2, physical layer n-1 represents a multi-band according to the present technology, and each band may have a frequency carrier (FC) size assigned to a specific service according to the predefined frequency policy. For example, physical layer 0 (RF carrier 0) may have the size of frequency band assigned to typical FM radio broadcast, and physical layer 1 (RF carrier 1) may have the size of frequency band assigned to mobile phone communication.
Though each frequency band may have a different frequency band size according to each frequency band characteristic as described above, for the sake of convenience of explanation, it is assumed in the following description that each frequency carrier (FC) has an “A” [MHz] size. Furthermore, each frequency allocation band may be represented as a carrier frequency for using a baseband signal at each frequency band, and thus hereinafter, each frequency allocation band will be referred to as a “carrier frequency band” or simply a “carrier” representing each carrier frequency band unless confused.
In addition, the aforementioned carrier may be referred to as a “component carrier” to distinguish it from a subcarrier, which is used in a multicarrier scheme as in a recent 3GPP LTE-A.
From this point of view, the foregoing “multi-band” scheme may be referred to as a “multi carrier” scheme or “carrier aggregation” scheme.
FIG. 2 is a view illustrating an example of the type in which multi carrier is used in a typical wireless communication system.
Referring to FIG. 2A, multi carrier in a typical technology may be a contiguous carrier aggregation, or may be non-contiguous carrier aggregation as illustrated in FIG. 2B. The unit for combining such carriers is a base bandwidth unit of a legacy system (e.g., LTE in case of a Long Term Evolution (LTE) Advanced system, and IEEE 802.16e in case of an IEEE 802.16m system), which is a typical technology.
In the multicarrier environment with a typical technology, there are defined two types of carriers as follows.
First, a first carrier (or primary carrier) refers to a carrier for performing the traffic of the terminal and base station, and the exchange of full physical layer and medium access control layer (PHY/MAC) control information. Furthermore, the primary carrier may be used for a typical operation of the terminal such as network entry. Each terminal has one primary carrier in a cell.
Furthermore, a second carrier (or secondary carrier) refers to a carrier that can be typically used for the exchange of traffic according to a base station specific allocation command and rule received from the first carrier. The second carrier may include control signalling for supporting a multicarrier operation.
In a typical technology, carriers in a multicarrier system may be divided into a fully configured carrier and a partially configured carrier based on the foregoing primary and secondary carrier.
The fully configured carrier refers to a carrier in which control signalling is configured. Furthermore, the information and parameters for multicarrier management and other carriers may be included in the control channels.
The partially configured carrier refers to a carrier in which all control channels for supporting downlink transmission in a downlink carrier with no uplink carrier constituting a pair in a time division duplex downlink (TDD DL) transmission or frequency division duplex (FDD) mode are configured.
Typically, the terminal may perform initial network entry through a primary carrier, and may exchange information on multicarrier capability to each other in the registration process by exchanging registration request/response (AAI_REG-REQ/RSP) messages with the base station.
In an MC operation in the current related art, the definition for a feedback channel allocation (HARQ ACK/NACK, CINR) method for an activated DL carrier is not defined.
In case of a carrier for which both DL/UL are in an active state, if a UL fastfeedback channel is assigned thereto through feedback allocation A-MAP IE transmitted to the DL A-MAP of the corresponding carrier, then the relevant feedback information can be transmitted through a UL feedback channel of the corresponding carrier. However, DL only activation is possible for the secondary carrier of an MC operation defined in the current standard such as IEEE 802.16m, and as a result, a UL control channel cannot be used in case of a DL only activated carrier.
Thus, when the terminal in a multicarrier mode (e.g., Basic MC mode, carrier aggregation mode, carrier switching mode) transmits and receives data through a DL only activated carrier, the standard such as IEEE 802.16m requires definition on whether a feedback channel for transmitting UL feedback information (e.g., CQI feedback, MIMO feedback, HARQ ACK/NACK feedback, or the like) should be assigned to which carrier's UL control channel.
In addition, when secondary carrier(s) assigned by the base station at the time of network (re)entry of the terminal has a different coverage, the corresponding carrier has a smaller coverage than that of the existing activated carrier if the base station unaware of the channel state of inactive carrier(s) indicates that any inactive carrier is to be activated, and the activation of the carrier may be failed if the terminal is not located in the coverage.
Due to this reason, feedback to a DL carrier such as CINR OR CQI to any secondary carrier is required to be transmitted to a particular inactive carrier as well as an active carrier.